Alcohol use among youth is related to traffic crashes, suicides and assaults. A promising approach for preventing youth from consuming alcohol and experiencing these problems is to prevent youth from obtaining alcohol. The Complying with the Minimum Drinking Age Trial (CMDA) was a five-year multi-community quasi- experimental trial designed to examine the effectiveness of two interventions targeting alcohol establishments-owner/manager training and law enforcement compliance checks-to reduce the propensity to sell alcohol to underage youth. Results showed that law enforcement compliance checks have an immediate effect on propensity to sell alcohol to underage youth (reducing the propensity by 17%), but this effect decays either completely or by 50% depending on the type of establishment, within a three-month period. We propose to conduct a two-year study to analyze secondary data from the CMDA trial to assess whether a pattern of law enforcement compliance checks exists that maximizes effects of the checks for reducing illegal alcohol sales to underage youth. We will use state-of-the-art geospatial techniques and hierarchical regression models to assess: (1) spatial autocorrelation of propensity for alcohol establishments to sell alcohol to underage youth;(2) extent to which effects of law enforcement compliance checks diffuse across space to impact the propensity of neighboring alcohol establishments to sell to underage youth;and (3) simultaneous impact of compliance checks across both time and space, including possible interactive effects of the two. Results from the statistical models will be used to generate a pattern or patterns of law enforcement compliance checks that optimize the effects of these checks on preventing underage sales. PUBLIC HEALTH RELEVANCE: Communities are interested in identifying cost-efficient, research-based methods for reducing youth access to alcohol, and subsequently reducing alcohol problems and related costs. Law enforcement compliance checks have been identified as an effective deterrent to sales of alcohol to underage youth. Findings from the proposed study will indicate how far the deterrent effects of compliance checks diffuse geospatially, providing guidance on how many establishments need to be checked within specific neighborhoods and at what frequency.